init / exit function ordering

The vlib init function subsystem now supports a mix of procedural and
formally-specified ordering constraints. We should eliminate procedural
knowledge wherever possible.

The following schemes are *roughly* equivalent:

static clib_error_t *init_runs_first (vlib_main_t *vm)
{
   clib_error_t *error;

   ... do some stuff...

   if ((error = vlib_call_init_function (init_runs_next)))
     return error;
   ...
}
VLIB_INIT_FUNCTION (init_runs_first);

and

static clib_error_t *init_runs_first (vlib_main_t *vm)
{
   ... do some stuff...
}
VLIB_INIT_FUNCTION (init_runs_first) =
{
    .runs_before = VLIB_INITS("init_runs_next"),
};

The first form will [most likely] call "init_runs_next" on the
spot. The second form means that "init_runs_first" runs before
"init_runs_next," possibly much earlier in the sequence.

Please DO NOT construct sets of init functions where A before B
actually means A *right before* B. It's not necessary - simply combine
A and B - and it leads to hugely annoying debugging exercises when
trying to switch from ad-hoc procedural ordering constraints to formal
ordering constraints.

Change-Id: I5e4353503bf43b4acb11a45fb33c79a5ade8426c
Signed-off-by: Dave Barach <dave@barachs.net>

src/plugins/crypto_openssl/main.c

@@ -232,13 +232,9 @@ crypto_openssl_init (vlib_main_t * vm)
   vlib_thread_main_t *tm = vlib_get_thread_main ();
   openssl_per_thread_data_t *ptd;
   u8 *seed_data = 0;
-  clib_error_t *error;
   time_t t;
   pid_t pid;
 
-  if ((error = vlib_call_init_function (vm, vnet_crypto_init)))
-    return error;
-
   u32 eidx = vnet_crypto_register_engine (vm, "openssl", 50, "OpenSSL");
 
 #define _(m, a, b) \
@@ -284,7 +280,13 @@ crypto_openssl_init (vlib_main_t * vm)
   return 0;
 }
 
-VLIB_INIT_FUNCTION (crypto_openssl_init);
+/* *INDENT-OFF* */
+VLIB_INIT_FUNCTION (crypto_openssl_init) =
+{
+  .runs_after = VLIB_INITS ("vnet_crypto_init"),
+};
+/* *INDENT-ON* */
+
 
 /* *INDENT-OFF* */
 VLIB_PLUGIN_REGISTER () = {